Starting in late September, the New York Times apparently began increasing how frequently it moved older articles off its "Most Popular" page, making room for newer articles to appear more rapidly on the list. Several bloggers have speculated that this is a "Digg Effect" of its own kind, where large, well-established sites take their cues from the success of younger sites like Digg. Digg.com already has over 75% as many page views at the Times as of July, 2007
Digg is well-known to have fresh articles appear on its home page by the minute, and this is part of its appeal. The NYT apparently noticed more visitors going to the most popular page and not clicking on any links, correctly surmising there wasn't anything new enough since the last time the visitor came to that page. This step by the Times follows their adding social media links to many articles in late in 2006 (Time Surrenders to Social News), shortly after Digg broke into the list of top 20 most visited sites on the web in barely over two years of operation (digg post on that news).
Some have hypothesized the Times may have begun testing after the Onion article 'Most E-Mailed' List Tearing New York Times' Newsroom Apart got their attention ...
It also appears the NYT may be watching the frequency of visits to the most popular page to try to fine tune how frequently new articles should appear on the list, in addition to surveying how often algorithms on other sites like digg cause new articles to appear.